I have never cultured them but (if my memory serves me right) read that the basic needs of tubifex are tons of food and flowing water to wash away their wastes and supply high concentration of oxygen. They do not seek food, only eat what is readily available to them.

Soil based tubs are better than plastic or other man made tubs. Size of tubs vary 1 x 0.5 x 0.25m to 2 x 1 x 0.3m. They mix mud/soil with organic fertilizers and let it age (sorry forgot how long) with just enough water (flowing is better). Once everything is ready, they put some tubifex in and increase water flow. Harvesting with this method IMO is troublesome because you will have to separate/clean the worms from the mud. Further you may get lots of bloodworms which in turn may prey on tubifex so covering might be a good idea .... just my thought.

Another method (Singapore breeders) is more simple - they make their water drainage like a spiral, the center being the outlet of waste water from water changes ect. They place the worms in small plastic baskets with holes in them, lined up inside the water drainage. Some how the worms will get to the outlet where there are lots of oxygen - this is where they harvest the worms. Local breeders have tried this method on a smaller scale using PVC pipes and claim to be successful.

Harvesting sounds much easier with this method - no mud. But I don't understand how they get food? ..... Are fish wastes adequate??? Further will the water constantly flow at a regular rate? These questions were not discussed.

*** both methods I got from local sites but forgot where so I can't link..... sorry. Further I forgot how long it takes to be harvested.

They eat organic matter - in this case, yes the ferts. The ferts must be ...... not sure how to say it .... become compos(?). If the ferts is new (still in the form of droppings) it will kill the worms instead.

Tubifex worms are as similar to Black worms but they're thinner, longer and more active and the water has to be rinsed daily, they like to stick together and make a ball shape, water level just enough to cover them. I use to feed them to my bettas a while back but I don't see them around anymore only back home in Hawaii